The invention concerns a process and a device for depicting the distribution of high activities of radioactive substances as is used in the diagnostic technique of whole-body scintigraphy. The subject of the invention concerns depicting the distribution of high activities of radioactive substances using a whole-body scintigraphic device having a camera or the like, such as a gamma camera or scanner.
To depict the distribution of radioactive substances in bodies, especially in nuclear-medicine diagnostics for survey photographs of the entire patient (whole-body scintigraphy), gamma cameras having a whole-body attachment, or gamma cameras specially designed as a whole-body device, are preferentially used. Here the collimated sensor-head is generally moved in one or more adjacent paths parallel to the patient's longitudinal axis. A difficulty with such processes and devices is that, in the case of distributions of high activities, counting-rate errors may occur owing to "pile-ups" and dead-time effects, just as with the use of scanners whereby the object is scanned line by line in one plane -- the focal plane -- by a probe provided with a focussing collimator. These "pile-ups" and dead-time effects cause an erroneous depiction of the distribution of radioactive substances.
The underlying problem of the invention is to create a process and a device of the aforementioned type whereby counting-rate errors of the aforedescribed type are avoided.
Using a process of the aforementioned type, the invention solves this problem by partially shielding the whole-body scintigraphic device from radiation incident upon the device as a function of the radiation intensity in order to optimize the counting rate. The device according to this invention provides features allowing for partial shielding of the whole-body scintigraphic camera as a function of the intensity of radiation incident upon the device.
Especially preferred embodiments of the process and of the device according to the invention are objects of the subclaims.
The invention is based on the surprising perception that the described disadvantages of the known processes and devices can be eliminated, otherwise than in the prior art, by optimizing the counting rate from photograph to photograph each time by partial shielding against the high-activity radiation incident upon an optimal region of the scintigraphic device. By contrast, a collimator, known from DE-OS No. 27 31 629, for generating tomographic sectional images, undertakes to uniformize the sensitivity over the entire field of view of the camera by partially providing the latter with shielding material, no thought being given to any adaptation, varying from photograph to photograph, of the counting rate to an optimal region. The DE-OS No. 0 083 756 pertains to a collimator with adjustable aperture, a collimator which in the case of processes and devices of the generic type would likewise not afford the desired counting-rate optimization. Known from U.S. Pat. No. 4,012,636 is a diaphragm that is used to generate the whole-body measuring field and to prevent so-called "zipper errors" when adjacent imaging paths overlap or when there are gaps between them, though here too the counting-rate reduction, proposed according to the invention, would remain unaddressed. Finally, the WO-OS No. 82/00897 shows a multitube collimator for a scintillation camera, a collimator in which the sensitivity and resolution can be influenced by modifying the collimator, though here too the principle of the counting-rate optimization according to the invention would remain unaddressed. Rather what this involves is the change in position between high resolution and high sensitivity, without having to change the collimator.